In high purity applications, it is common to use an orbital welding device, such as the device disclosed in U.S. Pat. No. 5,196,664 to McGushion (1993), to butt-weld together two components with annular cross sections, held together end to end by a clamping means. The components could include pipes, tubes, or tubular extensions protruding from components, such as regulators, valves, mass flow controllers/meters, or a wide variety of other similar components with a tube-like extension. Tube is used interchangeably for any of the above mentioned components.
The clamping means has primarily two sides, each side clamping one tube. Each side being normally comprised of two sections, top and bottom. Wherein the top and bottom are clamped together, with a tube interposed, lying within semicylinders formed through the mating faces of the top and bottom parts, or through interchangeable inserts fastened to the top and bottom. The semicylinder radius substantially matches the radius of the pipe. The semicylinder is designed to prevent significant lateral movement of the tube, relative to the semicylinder.
The two bottom sides are fastened together, with a spacer between them, bringing. The complete clamping means, including the two sides and the spacer, is assembled, and the tubes inserted between the top and bottom of each side. The top and bottom for each side can be hinged on one side to allow the top to swivel open, to receive the tube, the opposing side having a clamping mechanism, to draw the top down towards the bottom, engaging the tube. Alternately, the top portion can be separable from the bottom, with a camping means on both sides; or a latching means on one side and a clamping means on the opposing side.
The orbital welding device is inserted between the two sides, the sides straddling the C-shaped tip of the orbital welding device, the spacer being slightly thicker than the C-shaped tip. The electrode of the orbital welding device is substantially aligned with the seam, protruding from a C-shaped gear within the C-shaped tip. When welding, an arc is formed between the electrode and the seam of the tubes. The electrode orbits the seam, melting the parent material, resulting in the fusion of the two tubes at the seam.
Often, it is the case that two tubes in a complex system need to be welded together, in a very limited space, such as found in the semiconductor and aerospace industries. Therefore, for these applications, the orbital welders and clamping means are designed to occupy a limited space, preferably making them as small as possible. The thickness of the clamping means, as well as the overall dimensions, are often minimized, increasing compactness, but reducing overall strength.
When welding together long lengths of tubing or heavy components, the two sections, prior to welding, tend to exert a downward force, causing the top section on one or both sides to flex out, away from the seam. The outward flexure allows the two tubes to separate, causing a gap in the seam to form. On average, a gap of less 10% of the wall thickness can cause severe weld degradation. So, it is of great importance to eliminate this flexure to minimize or eliminate any significant gap.
The clamping means described previously allows for slight, but unacceptable, movement of the tubes during welding, because of its light construction. This is due to each of the top side pivoting outwardly in relation to the bottom sides. The hinges and clamping mechanisms fastening the top sides to the bottom sides cannot effectively prevent this skewing.
The resulting gap can degrade the weld, or cause it to fail completely. The ends of the two tubes need to be squarely butted one against the other, with minimal gap, continuously throughout the weld. An unacceptably wide gap in the seam can result in an uneven weld bead, having less parent material in that general area, or a an actual hole or permanent gap can be formed in the resulting cured weld bead. It can also result in a blowout of the weld, if an internal purge is utilized. All of these conditions, as well as others, can cause a weld to be rejected by quality control, costing an unacceptable loss in time and money.
To prevent a gap in the seam, several devices have been made to securely hold the tubes in abutment, resisting the pull exerted on the tubes. These designs, although preventing significant outward movement of the top sides, either introduce new undesirable effects or do not fully satisfy industry requirement. These requirements include: a clamping means that securely holds two tubes in abutment without significant gap, a lightweight clamping means, a clamping means that is compact and able to fit into confined spaces, and a clamping means that can operate with the tubes being clamped, one before the other, in any order, depending on what is immediately needed.
In an attempt to strengthen the clamping means, existing designs were made substantially larger than preceding designs. The overall size, thickness, and weight of the clamping means were increased. This heavy design decreased flexure and provided an allowable seam for which to weld. However, this heavy design was large, and could not be used in tight situations. Thus, the heavy design was limited in its applications. Additionally, the large, heavy clamping means design required a larger orbital welding device to mate effectively with the camping means during a weld. The overall size and weight of a setup increased significantly.
In another attempt to minimize fixture size and prevent outward flexure during the weld, a series of tack welds are applied around the seam, in a process called pre-tacking. Pre-tacking is a preliminary operation to the weld; therefore, requiring much more time to complete a weld.
Additionally, the presence of tack welds can be detected after the weld has been completed. Witness marks are evident in the finished weld, a thickening of the weld bead at the point of the tack weld. Since it is desirable to have a smooth, continuous weld bead, pre-tacking is not ideal. Moreover, pre-tacking often introduces additional impurities, compared to a continuous weld bead.
An additional existing design can be seen in U.S. Pat. No. 5,824,983 to Huddleston (1998). The bottom sides of the clamping assembly are affixed to the weld head; and the top sides are hinged to the bottom sides. The top sides are rigidly connected one to the other, across the top of the fixture, by a bracing plate.
Although this significantly reduces the outward flexing of the fixture, the design of the plate limits the usage of this device. Often, it is necessary to clamp one tube before the other in a welding setup; where one side of the clamping means is closed and fastened before the other. Huddleston, as well as other similar designs, are limited to clamping both sides simultaneously. When welding a tube to a stationary assembly of components, it is often more advantageous to clamp the assembly side of the tube junction, leaving the opposing clamping means side open. The clamping means, attached to the assembly, can be left in place, without being manually held, while the tube is prepared, and later clamped within the opposing side of the clamping means. Depending on clearance issues and individual setup needs for the preparation of each welding joint, it may be preferable to have either one of the sides closed before the other.
In other attempts to solve the problem of clamping means flexure, a bracing plate similar to Huddleston is employed. Instead of being fastened to both sides of the clamping means, synchronizing their actions, the bracing plate is fastened to just one side. The plate extends to the opposing side, engaging the opposing side with a clasping means, preventing both sides from outwardly flexing.
Again, this clasping device prevents flexure. However, the design restricts the use of the clamping means, a specified sequence of side closure. The side with the bracing plate attached, must be closed secondly, after the opposing side. Because the bracing plate is designed to engage the opposing side from above, this clamping sequence is required. This design would be difficult or impossible to use in restricted setups.
What is needed is a clamping means support for orbital tube welding that resists the outward flexure of the adjoining tubes, minimizing the gap in the seam formed between the tubes. What is also needed is a clamping means support that allows for either side of the clamping means to be engaged in any order, responding to each particular situation, and providing flexibility in use. What is additionally needed is a clamping means support that is lightweight and compact, able to be easily supported in close quarters by hand or by clamping one side to a stationary pipe assembly.